Gaseous sealing devices

ABSTRACT

A gaseous sealing device intended particularly for use with flare stacks. The device is composed of two hollow members disposed one within another and a number of walls extending between the members to form first and second chambers communicating with one another, the second chamber communicating with the interior of the innermost member open to the atmosphere. The first chamber receives a waste gas from the flare stack and the gas passes through the first chamber in one direction, through the second chamber in the reverse direction and finally through the innermost member again in said one direction. When the gas flow ceases air is prevented from passing into the first chamber by waste gas trapped in the device.

United States Patent [72] lnventor Ronald D. Wilkinson [73] Assignee Airoil BurnerCompany (GB) Limited West Drayton, Middlesex, England [32] Priority Mar. 21, 1968 [3 3 Great Britain 1 l 13721/68 [54] GASEOUS SEALING DEVICES 10 Claims, 3 Drawing Figs.

I so\ [56] References Cited UNITED STATES PATENTS 3,055,417 9/1962 Reed 431/202 3,289,729 12/1966 Reed 431/202 3,337,455 8/1967 Wilson et al. 23/277 Primary ExaminerEdward G. Favors Attorney- Linton and Linton ABSTRACT: A gaseous sealing device intended particularly for use with flare stacks. The device is composed of two hollow members disposed one within another and a number of walls extending between the members to form first and second chambers communicating with one another, the second chamber communicating with the interior of the innermost member open to the atmosphere. The first chamber receives a waste gas from the flare stack and the gas passes through the first chamber in one direction, through the second chamber in the reverse direction and finally through the innermost member again in said one direction. When the gas flow ceases air is prevented from passing into the first chamber by waste gas trapped in the device.

PATENTED mu 8 I97! INVENTOR RONALD DOUGLAS WILKINSON BY d /M ATTORNEYS GASEOUS SEALING DEVICES BACKGROUND TO THE INVENTION I Flare stack assemblies are well known in the petroleum and chemical industries, e.g. oil refineries, where their function is to burnoff or discharge a waste gas arising from a particular process. The waste gas may in fact consist of a mixture of gases. The waste gas is usually passed into a vertically disposed stack of considerable height and are discharged or burnt at the upper end of the stack by pilot burners. When a particular batch of waste gas has been discharged or burnt off or the flow of gas to the stack is interrupted air enters the upper end of the stack and moves downwardly therein. Thus, when the flow of waste gas is resumed the waste gas can mix with air which is present in the stack. The gas/air mixture thus forms an explosive combination within the stack which is dangerous.

In order to'overcome this problem a sealing device is known which is incorporated in the flare stack near the upper end thereof. The device is designed specifically for waste gases which have a molecular weight less than that of air. This known device has three concentric cylindrical parts through which the waste gas is made to pass in a flow path extending upwardly through the innermost part, downwardly through the gap between the innermostand inten'nediate parts and finally upwardly through the gap between the outermost and intermediate parts. The known device functions to trap a quantity of waste gas in the device in such a manner that the trapped gas serves as a seal to prevent air from entering the flare stack below the device.

In this device the gas flows through a number of relatively I small annular gaps which tend to act as a separator to knockout" liquid whichtends to condense in the device. The liquid that builds up as a result of the separation can eventually block the main inlet to the device and consequently such a device must be provided with a drain plug. It has been found, however, that in cold ambient weather conditions the liquid tends to freeze and consequently unless. a heating coil is incorporated into the device freezing of the liquid can totally disable the device and consequently the flare stack becomes inoperative. Furthermore, the device is somewhat difficult to construct since fairly stringent requirements are made regarding the dimensions of the particular chambers through which the waste gases flow. Y

A general object of the present invention is to provide an improved sealing device of the type generally described for use primarily but nor solely, with flare stacks.

SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a gaseous sealing device comprising a first hollow member, a second hollow member disposed within said first hollow member, one end of said second member being open to the surrounding and the other end of said second member being disposed within said first member, a closure closing an end of said first member adjacent said one end of the second member, at least three walls extending between said first and second members, a first chamber defined by a portion of the inner surface of said first member, by said closure and by two of said at least three walls; a second chamber defined by at least some of the remaining portion of the inner surface of said first member and by said at least three walls, the first and second chambers communicating adjacent said closure and said second chamber communicating with said second member at said other end thereof, a gas flow path extending through said first chamber in one direction, through said second chamber in the reverse direction and through the second member in said one direction and means for admitting gas into the device.

According to a further aspect of the invention there is provided a gaseous sealing device comprising two hollow members disposed one within another, one end of the innermost member being disposed within the outermost member, the other end of the innermost member being disposed externally of the outermost member and open to the surrounding atmosphere, a first wall positioned near said other end of the innermost member and extending between the innermost surface of the outermost member and the outermost surface of the innermost member to close the gap between the members, second and third walls extending between the innermost surface of the outermost member and the outermost surface of the innermost member to divide the gap between the members into two chambers communicating with one another near said first wall, a further wall extending across said one end of the innermost member and adjoining the innermost surface of the outermost member to close the gap between the members, a section being cut away from the innermost member adjacent said one end to form an inlet to the interior thereof.

The device made in accordance with this invention can be incorporated into a flare stack so that the outermost member is attached to a lower section of the stack and the innermost member is attached to an upper section of the stack. The transitions between the chambers are preferably smoothly constructed to prevent liquid knockout. An inlet pipe can be provided which communicates with the first'chamber and serves in use to allow the introduction of an oxygen free purge gas into the device to maintain the position of an interface between the trapped waste gas and the air which may enter the innermost member. 1 The hollow members may conveniently be cylindrical and coaxial. In a constructional embodiment of the device two walls extend from the inner surface of the outermost member and tangentially to the outermost surface of the innermost member to form the first and second chambers. A further wall extends between these walls and across the other end of the innermost members to adjoin a part of the innermost surface of the outermost member and a section is cut away from the innermost member adjacent said other end to provide an inlet thereto. A syphon tube can effectively extend from the second chamber to the first chamber in order to recirculate any liquid condensed in the device and this syphon tube can be conveniently located in a bore provided in the further wall. In order to maintain the interface between the air and trapped gas within a predetermined zone it is necessary to pass an oxygen-free purge gas into the device. The term oxygen-free, as used in this specification and claims means that the gas contains no oxygen or a small amount of oxygen below the explosive limit, generally recognized as about 0.5 percent by weight. The inlet pipe for admitting the purge gas can be disposed in a part of the device itself or in a lower section of the flare stack.

Various other aspects of the present invention will become more apparent from consideration of a constructional embodiment thereof.

BRIEF DESCRIPTION OF DRAWINGS A constructional embodiment of the present invention will now be described by way of example only,'with reference to the accompanying drawings wherein:

FIG. 1 is a perspective diagrammatic view of a device made in accordance with the present invention;

FIG. 2 is a diagrammatic sectional elevation of the device shown in FIG. 1; and

FIG. 3 is a cross-sectional plan view taken along the line A-A of FIG. 2.

DESCRIPTION OF THE EMBODIMENT As shown in the drawings, the device basically consists of two concentric cylindrical members, namely cylindrical outer member 10 and a cylindrical inner member 11. The outer member 10 has a frusto'conical elements or portions l2, 13 at its upper and lower end which taper to upper and lower'cylindrical portions 14, 15 respectively which can be attached to sections of a flare stack near the upper end thereof. The portions 14, 15 would adjoin upper and lower sections of the flare stack. Alternatively, the portions 12, 13 can be attached directly to the flare stack sections.

The inner member 11 is conveniently of the same diameter as the upper portion 14, i.e. the uppermost section of the flare stack. ln this example an inlet pipe 40 is provided which communicates with the interior of the portion 15. The pipe 40 serves to admit a purge gas into the portion 15, but it is to be understood that the inlet pipe 40 can be provided in the lower section of the stack or at any other convenient position upstream of the seal of the device described hereinafter.

Two walls 16, 17 extending substantially perpendicularly to one another are arranged tangentially of the inner member 1 l and are attached to the inner surface of the outer member as by welding. Although the device has been shown with tangential walls l6, 17 it is not necessary for the walls to be tangential and in certain constructions, perhaps of smaller size, these walls may extend radially of the inner member 11. An arcuate shaped base wall 18 is connected across the open end of the inner member 11 and is attached to each of the walls 16, 17 again as by welding. This wall 18 is conveniently located at the widest end of the lower frustoconical portion 13. The wall 18 is provided with a bore 19 communicating with an inlet 20 of a syphon tube 21. The outlet end 22 of the tube 21 is disposed beneath the wall 18 in the chamber defined inside the lower frustoconical portion 13.

A section is cut away from the lower end of the inner member 11 to form an inlet 23 of parabolic shape.

The particular construction of the device provides three distinct chambers through which a waste gas flows. A first chamber designated is defined by a portion of the outer surface of the member 11 and by one side of the walls 16 and 17. A second chamber designated 31 is defined by the remaining portion of the outer surface of the member 11 and by the other side of the walls 16 and 17. A third chamber designated 32 is defined by the inner surface of the member 11.

In operation, a waste gas flows through the portion 15 adjoining the lower section of the flare stack, upwardly through the chamber 30, downwardly through the chamber 31 and finally upwardly through the chamber 32 and through the portion 14 adjoining the upper section of the flare stack to emerge for combustion therefrom. The gas can be burnt at an upper end of the upper section of the flare stack by pilot burners in the manner known per se. Alternately the gases could be released to the atmosphere by means of simple pipes or bent stack sections.

[f the flow of the waste gas is interrupted surrounding air will flow into the upper section of the stack and into the upper portion 14. 1f the waste gas is lighter than air the gas will decant into the atmosphere via the portion 14 and the gas is eventually replaced by air. In general, the portion 14 and the chamber 32 formed inside the member 11 can become filled or partly filled with air and in some circumstances the air can even pass into chamber 31. However, the natural buoyancy between the gas in the chambers 32 and 31 causes a gas seal to be produced therebetween, so that a quantity of air is supported by a quantity of waste gas effectively trapped in the device. The seal is characterized by an interface which is fonned between the air and waste gas but due to gas diffusion this interface is indefinite and to adequately maintain the interface it is desirable if a further purge gas, different to the waste gas, be admitted to the device through the inlet 40. This purge gas can be lighter or heavier than air but it must be oxygen-free as defined hereinbefore.

The exact position of the interface depends upon many factors and it can be disposed in the chamber 32 or 31. Generally it would be desirable if the interface be somewhere in the vicinity of the parabolic inlet end 23 of the member 11. The seal effectively prevents the air passing into the chamber 32 from reaching the chamber 30 and contacting the gas in the remainder of the flare stack.

It should be noted that the flow path of the gas through the device is generally smooth and continuous and there are no sharp bends which would tend to produce liquid knockout. The areas of the chambers 30 to 32 are generally of the same order of size but there is preferably some adjustment of these areas to allow for frictional losses as the waste gas flows through the device. In this respect it is desirable that the forward velocity of the gas through the device be the same as that through the stack. Any liquid condensed in the device is drained from the upper surface of the wall 18 by means of the syphon 21 and this liquid is effectively recirculated into the inflowing gas stream.

Under certain conditions a phenomenon known as blowback can occur in flare stacks, where the resumption of flow of a waste gas for burning causes the gas to burn back along the stack. However, with the device made in accordance with the present invention the presence of the wall 18 reliably prevents any gas from burning back along the stack.

I claim:

1. A gaseous sealing device comprising a first hollow member, a second hollow member disposed within said first hollow member, one end of said second member being open to the atmosphere and the other end of said second member being disposed within said first member, a closure closing an end of said first member adjacent said one end of the second member, at least three walls extending between said first and second members, a first chamber for receiving waste gas, defined by a portion of the inner surface of said first member, by said closure and by two of said at least three walls; a second chamber defined by at least some of the remaining portion of the inner surface of said first member and by said at least three walls, the first and second chambers communicating adjacent said closure and said second chamber communicating with said second member at said other end thereof, a gas flow path extending through said first chamber in one direction, through said second chamber in the reverse direction and through the second member in said one direction and means for admitting an oxygen-free purge gas into the device to maintain the position of an interface between trapped waste gas and air which may enter the second member from said one end thereof.

2. A gaseous sealing device comprising two hollow members disposed one within another, one end of the innermost member being disposed within the outermost member, the other end of the innermost member being disposed externally of the outermost member and open to the atmosphere a first wall positioned near said other end of the innermost member and extending between the innermost surface of the outermost member and the outermost surface of the innermost member to close the gap between the members, second and third walls extending between the innermost surface of the outermost member and the outermost surface of the innermost member to divide the gap between the members into two chambers communicating with one another near said first wall, a further wall extending across said one end of the innermost member and adjoining the innermost surface of the outermost member to close the gap between the members, a section being cut away from the innermost member adjacent said one end to form an inlet to the interior thereof.

3. A device according to claim 1, wherein the gas admitting means includes a source of purge gas communicating with said first chamber.

4. A device according to claim 1, wherein said two walls extend between the outer surface of the second member and the inner surface of the first member, the third wall of said at least three walls extends across said other end of the second member and adjoins a part of the innermost surface of the first member and a section is cut away from the second member adjacent said other end thereof to provide an inlet thereto.

5. A device according to claim 4, wherein each of said two walls extend tangentially of the outer surface of the second member.

6. A device according to claim 4, wherein each of said two walls extends radially of the outer surface of the second member.

7. A device according to claim 1, wherein a syphon tube extends between the first and second chambers.

8. A device according to claim 4, wherein a syphon tube extends between the first and second chambers and has an inlet formed by a bore in said third wall.

9. A device according to claim 1, wherein two frustoconical elements are'provided each having its widest end attached to one of the ends of the second member and having its narrowest end directed outwardly of the device, one of said member, at least three walls extending between said first and second members, a first chamber defined by a portion of the inner surface of said first member, by said closure and by two of said at least three walls; a second chamber defined by at least some of the remaining portion of the inner surface of said first member and by said at least three walls, said first and second chambers communicating adjacent said closure and said second chamber communicating with said second member at said other end thereof, a gas flow path extending through said first chamber in one direction, through said second chamber in the reverse direction and through the second member in said one direction. 

2. A gaseous sealing device comprising two hollow members disposed one within another, one end of the innermost member being disposed within the outermost member, the other end of the innermost member being disposed externally of the outermost member and open to the atmosphere a first wall positioned near said other end of the innermost member and extending between the innermost surface of the outermost member and the outermost surface of the innermost member to close the gap between the members, second and third walls extending between the innermost surface of the outermost member and the outermost surface of the innermost member to divide the gap between the members into two chambers communicating with one another near said first wall, a further wall extending across said one end of the innermost member and adjoining the innermost surface of the outermost member to close the gap between the members, a section being cut away from the innermost member adjacent said one end to form an inlet to the interior thereof.
 3. A device according to claim 1, wherein the gas admitting means includes a source of purge gas communicating with said first chamber.
 4. A device according to claim 1, wherein said two walls extend between the outer surface of the second member and the inner surface of the first member, the third wall of said at least three walls extends across said other end of the second member and adjoins a part of the innermost surface of the first member and a section is cut away from the second member adjacent said other end thereof to provide an inlet thereto.
 5. A device according to claim 4, wherein each of said two walls extend tangentially of the outer surface of the second member.
 6. A device according to claim 4, wherein each of said two walls extends radially of the outer surface of the second member.
 7. A device according to claim 1, wherein a syphon tube extends between the first and second chambers.
 8. A device according to claim 4, wherein a syphon tube extends between the first and second chambers and has an inlet formed by a bore in said third wall.
 9. A device according to claim 1, wherein two frustoconical elements are provided each having its widest end attached to one of the ends of the second member and having its narrowest end directed outwardly of the device, one of said frustoconical elements forming said closure and having its narrowest end adjoining the outer surface of the second member.
 10. A flare stack incorporating a gaseous sealing device, said device comprising a first hollow member connected to said stack, a second hollow member disposed within said first hollow member, one end of said second member being open to the atmosphere and the other end of said second member being disposed within said first member, a closure closing an end of said first member adjacent said one end of said second member, at least three walls extending between said first and second members, a first chamber defined by a portion of the inner surface of said first member, by said closure and by two of said at least three walls; a second chamber defined by at least some of the remaining portion of the inner surface of said first member and by said at least three walls, said first and second chambers communicating adjacent said closure and said second chamber communicating with said second member at said other end thereof, a gas flow path extending through said first chamber in one direction, through said second chamber in the reverse direction and through the second member in said one direction. 